The heart is the center of a person's circulatory system. It includes a complex electromechanical system performing two major pumping functions. The heart includes four chambers: right atrium (RA), right ventricle (RV), left atrium (LA), and left ventricle (LV). The RA draws deoxygenated blood from organs of the body and injects it into the RV through the tricuspid valve. The RV pumps the deoxygenated blood to the lungs through the pulmonary valve. The blood gets oxygenated in the lungs. The LA draws oxygenated blood from the lungs and injects it into the LV through the mitral valve. The LV pumps the oxygenated blood to the organs of the body, through the aortic valve, to provide the organs with their metabolic needs for oxygen. These mechanical pumping functions are accomplished by contractions of the myocardium (heart muscles). In a normal heart, the sinoatrial (SA) node, the heart's natural pacemaker, generates electrical impulses, called action potentials, that propagate through an electrical conduction system to various regions of the heart to excite myocardial tissues in these regions. Coordinated delays in the propagations of the action potentials in a normal electrical conduction system cause the muscles in various regions of the heart to contract in mechanical synchrony such that the pumping functions are performed efficiently.
The normal pumping functions of the heart, indicated by the normal hemodynamic performance, require a normal electrical system to generate the action potentials and deliver them to designated portions of the myocardium with proper timing, a normal myocardium capable of contracting with sufficient strength, and a normal electromechanical association such that all regions of the heart are excitable by the action potentials. A blocked or otherwise abnormal electrical conduction and/or deteriorated myocardial tissue cause dysynchronous contraction of the heart, resulting in poor hemodynamic performance, including a diminished blood supply to the heart and the rest of the body. The condition where the heart fails to pump enough blood to meet the body's metabolic needs is known as heart failure.
Because the pumping functions are mechanical functions, the hemodynamic performance is ultimately determined by the mechanical synchrony of the heart. For this and other reasons, there is a need for a direct assessment of cardiac mechanical dyssynchrony. The assessment serves as a direct measure of efficacy for a cardiac therapy restoring the cardiac mechanical synchrony.